Vibration pickup comprising a clamping sleeve

ABSTRACT

A vibration sensor having a pressure sleeve is described, in which the pressure sleeve ( 2 ) may be mounted under pressure on a component causing vibration. To detect a vibration signal, e.g., in the case of a knock sensor, a sensory system ( 7, 5, 6 ,) is held by a seismic mass above it on the outside of the pressure sleeve ( 2 ) via a screw connection on a contact face of the pressure sleeve ( 2 ) under an axial prestress in the direction of the sensory system. The seismic mass ( 8 ) has an inside thread and may be screwed onto the sensory system ( 7 ) to produce the axial prestress in the direction of the sensory system ( 7 ). A seismic mass ( 8 ) or the sensory system ( 7 ) has at least two opposing grooves ( 14, 15, 16; 18, 19, 20, 21 ) running radially opposite one another, so that the plastic may enter an interior space ( 17 ) between the sensory system ( 7, 5, 6 ,) and the pressure sleeve ( 2 ) during extrusion through these grooves.

BACKGROUND INFORMATION

[0001] The present invention relates to a vibration sensor having a pressure sleeve according to the preamble of the main claim.

[0002] German Patent Application 44 03 660 A1 describes a vibration sensor having a pressure sleeve which is used with knock sensors for monitoring the function of an internal combustion engine. This pressure sleeve is attached fixedly via a contact area to the component whose vibration is to be detected, in this case to the engine block of the combustion engine.

[0003] The vibration to be detected is the knocking sound of the engine during operation with this known arrangement, the sound being transmitted via the pressure sleeve to a piezoceramic disk as the actual sensor element with contact disks and insulating disks in between them which permit signal pick-up, thus generating an electric output signal suitable for analysis.

[0004] The type of mounting or clamping of this sensory system on the pressure sleeve and the mounting of the vibration sensor on the vibrating component have a great influence here on the method of manufacture as well as any false measurements and disturbances in operation. The clamping of the sensor element having a plurality of individual parts, e.g., with a spring and a seismic mass, is accomplished in the case of this known vibration sensor with a threaded ring, for example, which may be screwed onto a corresponding thread on the pressure sleeve.

[0005] In addition, a vibration sensor of the type described previously is also known from German Patent Application 195 24 147 A1, in which the threaded ring and the spring in the form of a spring head nut are described as a one-piece component. This spring head nut may then be screwed onto the thread on the pressure sleeve and is thus in direct contact with the seismic mass.

ADVANTAGES OF THE INVENTION

[0006] The vibration sensor described above having a pressure sleeve, the pressure sleeve being mountable under pressure with an initially concave base area on a component that is the source of vibrations, is improved upon to advantage according to the present invention by the fact that the seismic mass is provided with an internal thread and may be screwed onto the sensory system to produce the axial prestress.

[0007] With the proposed arrangement, for example, it is possible to mount a knock sensor on the engine block of an internal combustion engine inexpensively, because fewer individual parts are needed and in particular a lower overall axial height and a lower weight of the vibration sensor are feasible. Furthermore, omission of the plate spring, which is present in the known arrangement, also permits a more constant characteristic curve in detection of the sensor signal.

[0008] In a design of the vibration sensor having an injection-molded plastic housing around the pressure sleeve having a sensory system and the seismic mass, the seismic mass may have at least two grooves running radially opposite one another according to the present invention. Through these grooves the plastic may enter an interior space between the sensory system and the pressure sleeve during extrusion, thereby securing them, so this permits a compact arrangement that may be mounted in any position, e.g., on the engine block.

[0009] In another advantageous embodiment having an injection-molded plastic housing, the sensory system has at least two grooves running radially opposite one another; through these grooves the plastic may enter the interior space between the sensory system and the pressure sleeve during injection. Here again, any desired installation position is possible, but it is simpler and less expensive to manufacture a seismic mass without grooves. In both embodiments, the grooves are preferably provided on the two axial boundary surfaces of the seismic mass or the piezoceramic disk of the sensory system. They are advantageously offset by 90° between one face and the other.

[0010] An especially good effect is achieved in clamping the sensor element with the seismic mass if one or both axial boundary surfaces of the seismic mass are designed to be concave so that the axial wall thickness of the seismic mass becomes smaller toward the center.

[0011] A vibration sensor in which a base area of the pressure sleeve has a concave contour toward the inside radially before being mounted on a component may also be designed to advantage so that the contact surface for the sensor element on the pressure sleeve has a convex contour toward the inside radially before assembly. This contour is designed so that after assembly, at least the sensory system is largely in flat contact with the contact surface.

[0012] These and additional features of preferred embodiments of the present invention are derived from the claims as well as from the description and the drawing, the individual features each being implemented alone or in the form of subcombinations of several features in the embodiment of the present invention and also in other fields, representing advantageous patentable embodiments for which patent protection is sought herewith.

DRAWING

[0013] Embodiments of the vibration sensor having a pressure sleeve are illustrated in the drawing and are explained in greater detail in the following description;

[0014]FIG. 1 shows a section through a knock sensor housing as a vibration sensor having a pressure sleeve and a screw-on seismic mass having grooves;

[0015]FIG. 2 shows a detail of the seismic mass according to FIG. 1;

[0016]FIG. 3 shows a section through a knock sensor housing as a vibration sensor having a pressure sleeve and a screw-on seismic mass plus a sensory system having grooves;

[0017]FIG. 4 shows a detail of the seismic mass according to FIG. 3, and

[0018]FIG. 5 shows a top view of the sensory system according to FIG. 3 having grooves.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0019]FIG. 1 shows a vibration sensor in the form of a knock sensor for an internal combustion engine having an exterior plastic housing 1 in which a pressure sleeve 2 is located. In the area of its lower end, pressure sleeve 2 has a flange-like edge 3 by which it is in contact at its lower bottom surface 4 with the engine block (not shown here) whose vibration is to be detected.

[0020] The following parts are arranged on the outside circumference of pressure sleeve 2, starting from a lower contact face on flange-like edge 3: an insulating disk 5, a first contact disk 6, a piezoceramic disk 7 as the actual sensor element and above that a second contact disk 6 and a second insulating disk 5. A seismic mass 8 having an inside thread 9 is placed on this arrangement and may be screwed onto pressure sleeve 2 in the direction of piezoceramic disk 7.

[0021] Electric terminals 11 for contact disks 6 and flat-pin plugs 12 are injected in an integrated terminal part 10 of housing 1, which is produced by a plastic extrusion method in particular. Flat-pin plugs 12 are thus connected to the two contact disks 6, so there is an electric connection to the two sides of piezoceramic disk 7 via the two contact disks 6, and the electric voltage generated by a pressure on piezoceramic disk 7 in the axial direction may be picked up.

[0022] A fastening screw (not shown here) may be passed through a central recess or a borehole 13 in pressure sleeve 2 for fastening this knock sensor as a whole to the engine block of the internal combustion engine either directly or indirectly. In mounting the known sensor, the entire torque exerted by the fastening screw described above on pressure sleeve 2 is transferred via bottom face 4, i.e., no force acts on piezoceramic disk 7 as the sensor element due to the mounting.

[0023] A prestressing force acts here, generated by the pressure of screwed-on seismic mass 8. The prestressing force is selected so that axial forces that are at the limit of tolerability without any permanent deterioration of the electric signal are acting on piezoceramic disk 7, and it is largely independent of thermal expansion as well as unavoidable compression of pressure sleeve 2 in mounting. The pulses exerted by seismic mass 8 in proportion to the vibration of the engine are converted to charge pulses which may be analyzed in a suitable device.

[0024] In its lower area, seismic mass 8 has grooves 14 and 15, which are also clearly visible from the detail of seismic mass 8 according to FIG. 2. FIG. 2 also shows that in addition to grooves 14 and 15 radially opposite one another on one axial side of seismic mass 8, grooves 16 which are offset by 90° are also situated on the other axial side. During extrusion, through these grooves 14, 15 and 16 the plastic may enter an interior space 17 between piezoceramic disk 7 and pressure sleeve 2 to form housing 1.

[0025] In the embodiment according to FIGS. 3, 4 and 5, in contrast with the diagram according to FIGS. 1 and 2, seismic mass 8 is designed without grooves. The sensory system or piezoceramic disk 7 here has grooves 18, 19 and 20, 21 which are visible in the three views of piezoceramic disk according to FIG. 5. FIG. 5 also shows metallized surfaces 22, which provide electric contacting of piezoceramic disk 7 on the two surfaces opposing one another axially via contact disks 6. 

What is claimed is:
 1. A vibration sensor having a pressure sleeve, in which the pressure sleeve (2) is mountable under pressure on a component causing vibration, and having a sensory system (7, 5, 6,) and a seismic mass (8) located above it, which are on the outside of the pressure sleeve (2), under an initial axial stress that is applied to a contact face of a flange-like segment (3) of the pressure sleeve (2), using a screw connection, wherein the seismic mass (8) has an internal thread and may be screwed on, in the direction of the sensory system (7), to produce the axial prestress in the direction.
 2. The vibration sensor according to claim 1, wherein one of the axial boundary surfaces of the seismic mass (8) is designed to be concave so that the axial wall thickness of the seismic mass (8) becomes smaller toward the center.
 3. The vibration sensor according to claim 1, wherein both axial boundary surfaces of the seismic mass (8) are designed to be concave, so that the axial wall thickness of the seismic mass (8) becomes smaller toward the center.
 4. The vibration sensor according to one of claims 1 through 3, having an injection-molded plastic housing (1) which is formed around the pressure sleeve (2) having the sensory system (7, 5, 6) and the seismic mass (8), wherein the seismic mass (8) has grooves (14, 15, 16) on at least one side, through which the plastic may be introduced during the injection molding, into an interior space (17) between the sensory system (7) and the pressure sleeve (2).
 5. The vibration sensor according to one of claims 1 through 3, having an injection-molded plastic housing (1) which is formed around the pressure sleeve (2) having the sensory system (7, 5, 6,) and the seismic mass (8), wherein the sensory system (7) has grooves (18, 19, 20, 21) on at least one side through which the plastic may be introduced during the injection-molding, into an interior space (17) between the sensory system (7, 5, 6,) and the pressure sleeve (2).
 6. The vibration sensor according to one of claims 4 or 5, wherein at least two radial, diametrically opposed grooves (14, 15, 16) are provided.
 7. The vibration sensor according to one of claims 4, 5 or 6, wherein the grooves on both axial boundary surfaces of the seismic mass (8) or the sensory system (7) are offset 90° from each other.
 8. The vibration sensor according to one of the preceding claims, in which, prior to being mounted on a component the bottom surface (4) of the pressure sleeve (2) has a contour, which runs radially inward in a concave manner and may be changed by the pressure in mounting, wherein the contact face has a contour, which runs radially inward in a convex manner prior to mounting and is designed in such a manner that, after the mounting, at least the sensory system (7, 5, 6,) lies essentially flat on the contact face. 